{x+y=27 20x+30y=6.6 求x、y值?

{x+y=27 20x+30y=6.6 求x、y值? x+x+y+y+y=21 ,x+x+y+y+y+y+y=27 ,x ,y=? x+x+y+y+y=21 ,x+x+y+y+y+y+y=27 ,x ,y=? x+y=27 20x+30y=660 求x、y值 x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 化简 x / y(x+y) - y / x(x+y) = x(x+y)(x-y)-y(y+x)(y-x)=(x-y)( )填空 x+x=y+30 x+y=27 20y+xy=20x 1=x+y 2=20x+30y x+x+x+y=20 x+x+y=14 x=?y=? 40X+30Y=2200 X>20 Y x+y=20,x-y=10,y= y=x(x 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 y+10x=x+y+9 10y+x=y+10x+27 f(x,y)=x*x*x+y*y*y-9xy+27极值 {6/x+y+10/x-y=30 6/x+y-10/x-y=-1